A roller-coaster car speeds down a hill past point A and then rolls up a hill past boint B. (circular motion). The car has a speed of 20 m/s at point...

A roller-coaster car speeds down a hill past point A and then rolls up a hill past boint B. (circular motion). The car has a speed of 20 m/s at point A. if the track exerts a normal foce on the car of 2.06 x 10^4 N at this point what is the mass of the car? (be sure to account for gravitational force)